1 files changed, 82 insertions, 0 deletions
diff --git a/Python/emscripten_trampoline.c b/Python/emscripten_trampoline.c
new file mode 100644
index 0000000..2a80ec4
--- /dev/null
+++ b/Python/emscripten_trampoline.c
@@ -0,0 +1,82 @@
+#if defined(PY_CALL_TRAMPOLINE)
+
+#include <emscripten.h>             // EM_JS
+#include <Python.h>
+#include "pycore_runtime.h"         // _PyRuntime
+
+
+/**
+ * This is the GoogleChromeLabs approved way to feature detect type-reflection:
+ * https://github.com/GoogleChromeLabs/wasm-feature-detect/blob/main/src/detectors/type-reflection/index.js
+ */
+EM_JS(int, _PyEM_detect_type_reflection, (), {
+    return "Function" in WebAssembly;
+});
+
+void
+_Py_EmscriptenTrampoline_Init(_PyRuntimeState *runtime)
+{
+    runtime->wasm_type_reflection_available = _PyEM_detect_type_reflection();
+}
+
+/**
+ * Backwards compatible trampoline works with all JS runtimes
+ */
+EM_JS(PyObject*,
+_PyEM_TrampolineCall_JavaScript, (PyCFunctionWithKeywords func,
+                                  PyObject *arg1,
+                                  PyObject *arg2,
+                                  PyObject *arg3),
+{
+    return wasmTable.get(func)(arg1, arg2, arg3);
+}
+);
+
+/**
+ * In runtimes with WebAssembly type reflection, count the number of parameters
+ * and cast to the appropriate signature
+ */
+EM_JS(int, _PyEM_CountFuncParams, (PyCFunctionWithKeywords func),
+{
+    let n = _PyEM_CountFuncParams.cache.get(func);
+
+    if (n !== undefined) {
+        return n;
+    }
+    n = WebAssembly.Function.type(wasmTable.get(func)).parameters.length;
+    _PyEM_CountFuncParams.cache.set(func, n);
+    return n;
+}
+_PyEM_CountFuncParams.cache = new Map();
+)
+
+
+typedef PyObject* (*zero_arg)(void);
+typedef PyObject* (*one_arg)(PyObject*);
+typedef PyObject* (*two_arg)(PyObject*, PyObject*);
+typedef PyObject* (*three_arg)(PyObject*, PyObject*, PyObject*);
+
+
+PyObject*
+_PyEM_TrampolineCall_Reflection(PyCFunctionWithKeywords func,
+                                PyObject* self,
+                                PyObject* args,
+                                PyObject* kw)
+{
+    switch (_PyEM_CountFuncParams(func)) {
+        case 0:
+            return ((zero_arg)func)();
+        case 1:
+            return ((one_arg)func)(self);
+        case 2:
+            return ((two_arg)func)(self, args);
+        case 3:
+            return ((three_arg)func)(self, args, kw);
+        default:
+            PyErr_SetString(PyExc_SystemError,
+                            "Handler takes too many arguments");
+            return NULL;
+    }
+}
+
+#endif